In container filling processes such as canning or bottling lines, it is often useful to monitor characteristics of the containers being filled. For example, the levels to which containers have been filled may be monitored for quality control purposes.
It is known to use a radiation source and a detector to determine the fill level of a container. For example, Schiessl et al., U.S. Pat. No. 4,481,595, describes a system that passes containers through a gamma radiation beam projected from a beam source to a detector. As a container passes through the beam, the system counts radiation pulses received by the detector. Once the entire container has passed through the beam, the system determines the average rate at which radiation pulses were received by the detector and compares this rate to a reference rate. Based on this comparison, the system produces a signal indicative of whether material in the container is at a high enough level to attenuate the beam. The system can be configured to detect underfill conditions by orienting the source and detector so that detected pulses pass through the container at a level below the expected fill level. Similarly, the system can be configured to detect overfill conditions by orienting the source and detector so that detected pulses pass through the container at a level above the expected fill level.